The present invention relates to a method of controlling electronic fuel injection to an internal combustion engine and, more particularly, to a method of controlling fuel injection having high reliability which enables an engine to be constantly driven without being stopped by a trouble of a part of an electronic circuit.
The number of electronic parts mounted on an automobile has recently been increased, which tendency involves a fear of lowering the reliability of a car as a whole. If an electronic part of a fuel injection system is out of order and the engine is stopped, it is not easy to trace the fault and repair on the road, so that there is no alternative but to call a mechanic. If a trouble is caused in an unfrequented place, it puts a fellow passenger to much trouble. Furthermore, if a trouble which makes it impossible to run the car is caused while carrying a very important person even in a big city, there is a fear of incurring a great social and economical loss.
A conventional mechanical supply system composed of a carburetor scarcely causes sudden trouble and, in most cases, malfunction is gradually sensed and foreseen, so that the reliability of the carburetor system is secured by preventive maintenance and routine checkup. As to the reliability of electronic parts, if initial failure is eliminated by accelerated test, there remains only a probability of the rest of the parts generating random failure. In order to prevent the breakdown of the whole system due to a random failure of an electronic part which constitutes an electronic circuit, a method of allowing redundancy on the level of parts, circuits and system is often adopted.
A method of allowing redundancy on the level of parts and circuits is lacking in practicality because cost is raised due to increase in the number of parts, the decision circuit for judging the quality of parts and circuits is not always reliable, and the system becomes complicated by the incorporation of a defective part identifying circuit and an alarm circuit. If a redundancy system is adopted, a defective part must be replaced immediately in order to preserve the characteristic of the redundancy system. In order to maintain the reliability, it is desirable that immediately after a trouble is caused, a certain extent of burden is put to the driver, thereby urging the driver to replace the defective part.